DYNAMIC CA STORAGE OF APPLES: MONITORING OF THE CRITICAL OXYGEN CONCENTRATION AND ADJUSTMENT OF OPTIMUM CONDITIONS DURING OXYGEN REDUCTION

The calculated respiratory quotient (RQ), based on respiration measurements, as well as the measurement of the chlorophyll fluorescence have been tested to detect the critical oxygen concentration known as anaerobic compensation point (ACP) during oxygen reduction in dynamic CA-storage (DCA). Apples of the ‘Braeburn’, ‘Idared’, ‘Maigold’, ‘Elstar’ and ‘Golden Delicious’ (2 harvest dates) varieties were stored in a flow-through system, where oxygen was decreased by steps until the critical level was reached. Both methods based on RQ and fluorescence signal F-α monitoring yielded identical oxygen values for ACP. The ACPs measured were at concentrations as low as 0.15-0.40 kPa, depending on the apple variety. ‘Braeburn’ at 0.4 kPa exhibited a higher critical oxygen level than the other varieties tested (0.15-0.30 kPa). After the critical oxygen limit was reached, the oxygen concentration was increased by about 0.1-0.3 kPa above the critical limit. In this way, the fruit were kept at oxygen levels of 0.3 kPa to 0.6 kPa for 200 days without causing physiological disorders. Fruit firmness values of DCA stored apples were generally significantly higher than in control LO stored fruit after a storage period of more than 200 days. Trials with ‘Golden Delicious’ (2 harvest dates) during 2 storage seasons showed that the rate of oxygen reduction, within the setup of the trials, had no influence on the level of ACP nor the fruit quality after storage. During oxygen reduction, the CO₂-concentration was held at a constant level recommended for ULO storage for one option while, for the other, CO₂-concentration was decreased proportionally to the oxygen concentration. Both variants resulted in identical values for ACP and fruit quality in terms of fruit firmness after storage.